Suzaku Announcement of Opportunity (AO-10)
Tadayuki Takahashi (Project sub-manager, ISAS/JAXA)
Hideyo Kunieda (Project scientist, Nagoya University)
The X-ray Astronomy satellite Suzaku was developed under the collaboration of Japan and the United States, and was launched by ISAS/JAXA on 2005 July 10. Suzaku has successfully carried out astronomical observations using the X-ray Imaging Spectrometer (XIS) and the Hard X-ray Detector (HXD). Starting in 2006 April, we have carried out observations based on proposals received from researchers all over the world. Many observations based on these proposals have resulted in numerous publications that take advantage of the wide-bandpass, high-sensitivity, moderate spectral resolution capabilities of Suzaku. In the mean time, however, the the amount of electric power supply by the Solar Array Paddle (SAP) has decreased noticeably starting in late 2011. Although we have recovered our ability for routine observations for a while, the situation worsened again in 2014, due to the secular decline of the battery capacity. Due to the performance decline of both SAP and the batteries, it is now rare for us to be able to operate both XIS and HXD.
We, the Suzaku project, have continued to monitor the power situation carefully. We have not seen noticeable decline in available power since 2014 July. Therefore, we have decided to proceed with this announcement of opportunity (AO-10), even though there will be a limitation on the instruments that can be operated. Note that we cannot guarantee that further degradation of the power situation will not occur during the AO-10 period. We therefore invite the community to submit observing proposals, while noting the following.
- The period of AO-10 observations will be 6 months from 2015 May 1 to October 31.
- We solicit only observations using XIS. When the Suzaku orbit is such that the satellite is in orbital day for a higher fraction of the time than average, we will operate HXD and XIS simultaneously, but this will be possible only for a small subset of the time. We therefore will not accept any proposals for which the use of HXD is necessary.
- While we will not spare any effort to continue Suzaku observations, one countermeasure in case the power situation degraded further will be to reduce the number of XIS units in operation from 3 to 1. If we take this option, then we will increase the exposure times of accepted observations by a factor of 3.
- We do not solicit Key Project proposals.
In addition, we plan to continue the Suzaku-Fermi joint program initiated in AO-6, through the Fermi Guest Investigator program. Please refer to the Fermi web page for further details. In contrast, we will not continue the joint Suzaku-Chandra program initiated in AO-4.
In addition, we note that continuation of Suzaku observations beyond 2015 July is also contingent on the results of the ISAS review to extend Suzaku operation.
This call for proposals is applicable to scientists based in the US.
Scientists in ESA member countries should consult the version at ESA, while scientists in all other countries, including Japan, should consult the version at ISAS/JAXA.
2. The Suzaku Observatory
The Suzaku satellite carries four modules of the X-Ray Telescope (XRT) that focus X-rays up to ~10 keV with high efficiency, each with an X-ray CCD camera (XIS) module. Three XIS units are currently active. The XIS is particularly suitable for studies of extended sources, and the use of charge injection since AO-2 has limited the degradation of energy resolution. The technical description of the Suzaku instruments and the list of targets that have been observed or accepted can be found through the Suzaku Guest Observer Facility homepage.
While it may be possible to use the non-imaging hard X-ray detector (HXD) covering 10-600 keV, depending on the availability of sufficient power, such periods are very limited and unpredictable. Therefore, we do not accept proposals that require the use of HXD data.
3. Mission Phases and Time Allocation
Observing time during AO-10 will be allocated based on proposals from the community, as has been the case since 2006 April. This refers to 87% of total time, excluding:
- Observatory Time (3%) for satellite maintenance and related purposes
- Calibration time (5%) for ongoing calibration of the instruments; and
- Director's Discretionary Time (DDT; 5%) for observations of gamma-ray bursts or any genuinely unpredictable events, and other important observations granted at the discretion of the mission director. This specifically includes observations based on MAXI trigger.
We estimate 38 ksec of good time per day, so the time available to the proposers is 5951 ksec (38 ksec x 180 x 0.87). During AO-10, this is distributed as follows.
|(1)||Japan time||2975 ksec (ESA 476 ksec, Japan and others 2499 ksec)|
|(2)||US time||2332 ksec|
|(3)||Joint Japan-US time||744 ksec|
Here the Japan time includes joint Japan-ESA time, which amounts to 476 ksec. Accordingly, the remaining 2499 ksec is the time for Japanese scientists in AO-10. All proposals from outside Japan, US and ESA should be submitted to the Japan time. Note, however, that the total approved exposure time of proposals whose principal investigators (PIs) are not Japanese nor from ESA member states is not to exceed the joint Japan-ESA time. The joint Japan-US time will be used if proposals for the same targets are accepted both in Japan and US, and if both PIs accept such merging (the proposal form has a check box for the PI to indicate whether he/she accepts the merging). Observation time from Suzaku-Fermi joint programs is included in one of the above nationality-based categories, depending on the PI's affiliation.
4. Proposal Policies
(1) Only researchers based in the US and affiliated with a US institution are eligible to submit their proposals to NASA as the PI. In rare cases, a single PI may be considered eligible to submit Suzaku proposals through multiple agencies. Such a PI must, however, choose a single agency for all his/her AO-10 proposals; it is forbidden for a single PI to submit proposals to multiple agencies during a single cycle, even if they are for independent projects. On the other hand, there can be co-Investigators from any countries in proposals submitted to NASA.
(2) The complete list of targets accepted through AO-9 can be found in the Timeline & Mission Information section of the Suzaku GOF site. The observations of priority A and B targets are guaranteed. New proposals for these targets will not be approved without an explicit justification for an additional observation, such as much longer exposure, different pointing position on the same extended object, or a different phase of a variable object. Given the possibility that AO-10 is the final general call, proposals which are similar to past observation programs are welcome if the new data are expected to strengthen past results. These include, for example, enhancement of statistics of a certain object by simply adding exposure time, completing a mapping observation to cover the entirety of a diffuse object, and increasing the number of samples from a certain source category. In addition, the next generation X-ray observatory ASTRO-H will be launched in the Japanese fiscal year 2015 which ends in March 2016. Proposals which are designed to enhance the outcome of future ASTRO-H observations are particularly welcome.
On the other hand, some of the priority C targets and TOO targets have not been observed. This can be checked at this page at ISAS.
Any PI can submit proposals for the C or TOO targets that are unobserved. It must be noted, however, that unobserved AO-9 C or TOO targets may be observed by the end of AO-9 period (to be extended through April 2015). In this case, the observations of the C targets are regarded as being completed if the exposure time exceeds 70% of the proposed time. If the exposure time is less than 70 %, on the other hand, an additional observation will be carried out to fill the remaining time only if a proposal for the same target from the same PI is accepted at a higher priority (A or B) in AO-10. Otherwise, the observation carried out in AO-9 is ignored, and the target is open for competition in AO-10.
(3) The exposure time of the observation should be justified based on the specific scientific objectives, preferably using simulations. The project team sets the minimum exposure time of a single pointing observation at 10 ksec, considering the observation efficiency. There is no formal upper limit for observing time that can be requested. Note that any observations based on a proposal whose approved total observation time exceeds 300 ksec are open to the public as soon as the data are ready for analysis (no proprietary is awarded to the proposer). Very long observations naturally require a higher degree of scientific importance to be accepted.
(4) A continuous observation of a single target is guaranteed for up to 100 ksec. This limitation originates from the Moon light constraint to the star trackers' field of view, conflict with other time critical observations, and other operational/planning difficulty. The operation team accepts requests for uninterrupted observations longer than 100 ksec, but these will be carried out on a best-effort basis.
(5) Target of opportunity (TOO) proposals are allowed for short-lived events on known objects whose timing is uncertain. This category is referred to as "Reserved TOO observation.". In this case, the condition to trigger the observation, the estimated probability of the event to take place during the AO-10 period, and the expected duration of the event should be specified in the proposal, as well as other information required for non-TOO observation proposals. Any proposal that does not name a specific target, such as "Observation of a forthcoming nearby supernova," or "next nova explosion in M31," will not be accepted. The number of potential targets for a TOO proposal is limited to at most 5 per proposal. The scientific justification of TOO proposals must specify how many targets should be observed (the number of "triggers") to fulfill the scientific goals of the proposal. If the total exposure time to complete the requested number of targets is equal to or larger than 300 ksec, the data will be open to public as soon as the first observation is finished. See (3) above.
(6) It is possible to submit proposals specifying the time of observations as TC (Time Critical) observations. These include observations of a specific binary phase, coordinated observations with other wavebands, monitoring a target several times with certain time intervals, roll-angle-constrained observation of diffuse sources, and so on. Multi-pointing observations of a variable target (even with no other constraints, such as "3 separate observations any time during the AO-10 period") are also considered TC. So is a background observation to be carried out close to the time of the main target observation. The Suzaku operation team will do their best to perform the observations as requested. In all these cases, the PI must check the TC flag in the target form. Even if the coordination with other instruments is not planned in detail at the time of the proposal submission, the PI is required to check the TC box if he/she would like to do so after the approval of the proposal. An observation without a TC flag is treated as non-TC observation, and the coordinated observation can only be carried out if the other telescopes follow the Suzaku schedule.
(7) Any genuinely unpredictable events, such as gamma-ray bursts and supernovae, can be observed as part of the DDT ("realtime TOO observation"). Proposals for realtime TOO observations are accepted at any time outside the selection process of ordinary proposals. See this ISAS page for further details. There are no proprietary data rights for realtime TOO observations. Note that real-time TOO proposals for gamma-ray bursts can be accepted from any investigators starting in AO-7.
(8) The Suzaku project will accept proposals using P-sum/timing mode for the XIS, as well as the normal imaging mode. In the P-sum/timing mode, photon pile-up is unimportant, and a time resolution as fast as 7.8 msec can be achieved, although only 1-dimentional images can be obtained. Note, however, that the P-sum/timing mode can be used only for XIS3, and neither Spaced-row Charge Injection nor CTI correction can be applied, and hence the energy resolution is significantly worse than in the normal imaging mode. In addition, the calibration accuracy is not as good as in the normal imaging mode. Refer to the technical description document for details on the P-sum/timing mode.
(9) The project team has supported two default aim points since AO-1: the XIS nominal and the HXD nominal positions. Of them, the team ceased to support the HXD nominal position as of AO-7. As a result, the standard response matrices will not be provided for the HXD nominal pointing. No observations with non-standard readout clocks (P-sum/timing mode and window/burst options) will be carried out at the HXD nominal position. Note, however, that the operation team does not prohibit observations at the HXD nominal point with a standard XIS mode, at the proposers' own risk.
5. Review Process and Schedule
Researchers based in the US and affiliated with a US institution should submit their proposals to NASA. The deadline is 2015 February 3 at 4:30 pm EST for proposals submitted to NASA. After the US national review, a Japan-US merging committee will be convened in mid April, 2015, and the final observing program will be published soon thereafter.
Accepted targets will be classified into three categories (A, B, and C) based on proposal ranking. Priority A targets will be preferentially observed during the AO-10 period (2015 May to September), and the observation are regarded as completed if the exposure time is more than 90% of the requested time. Priority B targets will be scheduled in this period as much as possible, but may be carried over to the next cycle. Observations of the priority B targets are regarded as completed if the observation covers more than 70% of the requested time. Priority C targets will be used as fillers when there are gaps in the schedule. Of the total available time T (=5951 ksec = 180 d x 38 ksec/d x 0.87), we will accept 0.6T (=7141 ksec), 0.3T (=3571 ksec) and 0.5T (=5951 ksec) for A, B, and C proposals. This implies an oversubscription fraction of 40%. Oversubscribed targets will be scheduled if observing time remains after the observatory time, the calibration time, and DDT are assigned.
Reserved TOOs and time critical observations pose constraints on Suzaku operation. Hence the total fraction of them is limited to be some 15% of the total available time. Note that we will review this fraction at the time of the merging committee meeting (mid April 2015), based on the up-to-date prospect of the SAP power supply degradation information.
6. Data Rights
Normally, proposers of regular proposals have proprietary rights to the data for 1 year after receipt of the processed data. This does not apply to the data based on the proposals whose total exposure time (including those for priority C targets) is equal to or more than 300 ksec.
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